Methods and precursors for manufacturing a perforated composite part

ABSTRACT

Precursors, and methods for manufacturing perforated composite parts, an exemplary precursor including structural fibers embedded in a cured matrix material and interposed between two removable plies, where the precursor may also have a sacrificial fiber extending through the removable plies, the matrix material and between the structural fibers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/523,991 filed on May 3, 2017 as the U.S. National Phase ofInternational Patent Application Number PCT/GB2015/053290 which wasfiled on Nov. 2, 2015 claiming priority to British Patent ApplicationNumber GB 1419529.1 filed on Nov. 3, 2014, all of which saidapplications are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The disclosure relates generally to manufacturing composite parts, andmore particularly to manufacturing parts such as composite facing sheetsof acoustic attenuation devices using sacrificial fibers.

BACKGROUND OF THE ART

Reducing aircraft noise is important to the growth of air transport andfor improving the quality of life of people living near airports. Thenoise associated with an aircraft can be produced from various sourceson the aircraft and by various mechanisms. For example, a fan of aturbofan aircraft engine can be a dominant source of noise duringtake-off and landing of an aircraft having modern high-bypass ratioturbofan aircraft engines.

The use of noise attenuating devices inside aircraft engines is known.Existing noise attenuating devices can be designed to achieve a desiredacoustic performance. However, designing and manufacturing such noiseattenuating devices to the specifications required to achieve thedesired acoustic performance can be difficult, time-consuming andexpensive.

Improvement is therefore desirable.

SUMMARY

In one aspect, the disclosure describes a method for manufacturing aperforated composite part. The method comprises:

-   -   producing a precursor comprising structural fibers embedded in a        cured matrix material and interposed between two removable        plies, the precursor also comprising a sacrificial fiber        extending through the removable plies, the matrix material and        between the structural fibers;    -   removing at least one of the removable plies from the precursor;        and    -   removing the sacrificial fiber from the precursor after removing        the at least one of the removable plies to form a through hole        in the precursor at a location of the sacrificial fiber.

Removing the sacrificial fiber may comprise causing the sacrificialfiber to disintegrate.

Removing at least one of the removable plies may cause an end of thesacrificial fiber to become exposed to facilitate disintegration of thesacrificial fiber.

Removing at least one of the removable plies may cause severing of thesacrificial fiber.

The method may comprise removing the sacrificial fiber after removingboth of the removable plies.

Removing the sacrificial fiber may comprise causing evaporation of thesacrificial fiber.

The sacrificial fiber may comprise a thermoplastic aliphatic polyester.

The sacrificial fiber may comprise a polylactide (PLA).

Removing the sacrificial fiber may comprise causing dissolution of thesacrificial fiber.

The sacrificial fiber may comprise one of: polyacrylamides,polyacrylates, acrylamide-di methylaminoethyl acrylate copolymers,polyamines, polyethyleneimines, polyamidoamines and polyethylene oxide.

The sacrificial fiber may comprise one of: water soluble polyethyleneoxide, hydrolysed cellulose acetate and polyvinyl alcohol.

The sacrificial fiber may be coated with an agent that hinders achemical reaction between the sacrificial fiber and the matrix material.

The structural fibers may be part of a non-crimp fabric.

The removable plies may comprise a polytetrafluoroethylene-coatedfiberglass fabric.

The method may comprise peeling the removable plies from the precursorto cause severing of the sacrificial fiber.

In another aspect, the disclosure describes a method of manufacturing aperforated composite part using a precursor comprising structural fibersembedded in a cured matrix material and interposed between two removableplies where the precursor also comprises a sacrificial fiber extendingthrough the removable plies, the matrix material and between thestructural fibers. The method comprises:

-   -   removing the removable plies from the precursor; and    -   removing the sacrificial fiber from the precursor after removing        the removable plies to form a through hole in the precursor at a        location of the sacrificial fiber.

Removing the sacrificial fiber may comprise causing the sacrificialfiber to disintegrate.

Removing the removable plies may cause ends of the sacrificial fiber tobecome exposed to facilitate disintegration of the sacrificial fiber.

Removing the removable plies may cause severing of the sacrificialfiber.

Removing the sacrificial fiber may comprise causing evaporation of thesacrificial fiber.

Removing the sacrificial fiber may comprise causing dissolution of thesacrificial fiber.

The method may comprise peeling the removable plies from the precursorto cause severing of the sacrificial fiber.

In a further aspect, the disclosure describes a precursor formanufacturing a perforated composite part. The precursor comprises:

-   -   a layup having a first face and an opposite second face, the        layup comprising structural fibers embedded in a cured matrix        material and interposed between the first face and the second        face; and    -   a sacrificial fiber extending through the layup and through the        first face and the second face of the layup, the sacrificial        fiber being removable from the layup in order to form a through        hole in the layup at a location of the sacrificial fiber; and    -   a fiber severing member removably attached to the layup and        configured to sever the sacrificial fiber upon removal of the        fiber severing member from the layup.

The fiber severing member may comprise a first removable outer plydisposed against the first face of the layup. The precursor may comprisea second removable outer ply disposed against the second face of thelayup.

The fiber severing member may be configured to not chemically bond withthe matrix material.

The fiber severing member may comprise a polytetrafluoroethylene-coatedfiberglass fabric.

The sacrificial fiber may be coated with an agent that hinders achemical reaction between the sacrificial fiber and the matrix material.

The structural fibers may be part of a non-crimp fabric.

The sacrificial fiber may be configured to evaporate at a temperaturethat is not otherwise detrimental to the structural fibers or to thematrix material.

The sacrificial fiber may comprise a thermoplastic aliphatic polyester.

The sacrificial fiber may comprise a polylactide (PLA).

The sacrificial fiber may be configured to be dissolved using a solventthat is not otherwise detrimental to the structural fibers or to thematrix material.

The sacrificial fiber may be water-soluble.

The sacrificial fiber may comprise one of: polyacrylamides,polyacrylates, acrylamide-di methylaminoethyl acrylate copolymers,polyamines, polyethyleneimines, polyamidoamines and polyethylene oxide.

The sacrificial fiber may comprise one of: water soluble poly(ethyleneoxide), hydrolysed cellulose acetate and polyvinyl alcohol.

Further details of these and other aspects of the subject matter of thisapplication will be apparent from the detailed description and drawingsincluded below.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Reference is now made to the accompanying drawings, in which:

FIG. 1 is a partial axonometric view including a cutaway portion of anexemplary noise attenuating device;

FIG. 2A is a partial cross-sectional view of the noise attenuatingdevice of FIG. 1 taken along line 2-2 of FIG. 1 showing exemplary holesthrough a composite perforated facing sheet of the device according toone embodiment;

FIG. 2B is a partial cross-sectional view of the noise attenuatingdevice of FIG. 1 taken along line 2-2 of FIG. 1 showing other exemplaryholes through the composite perforated facing sheet of the deviceaccording to another embodiment;

FIG. 3 is a schematic cross-sectional representation of an exemplaryprecursor used in the manufacturing of the perforated composite facingsheet of the noise attenuating device of FIG. 1;

FIG. 4 illustrates exemplary cross-sectional shapes for a sacrificialfiber inserted into the precursor of FIG. 3;

FIG. 5 is an exploded view of an exemplary layup of structural fibersand two removable outer plies of the precursor of FIG. 3;

FIG. 6 illustrates the application of an exemplary stitch of asacrificial fiber through removable outer plies and also throughstructural fibers of the precursor of FIG. 3;

FIG. 7 is an axonometric view of the exemplary stitch of the sacrificialfiber applied in accordance with the stitching method illustrated inFIG. 6;

FIG. 8 illustrates the application of another exemplary stitch of asacrificial fiber through removable outer plies and also throughstructural fibers of the precursor of FIG. 3;

FIGS. 9A, 9B and 9C respectively show a top, a cross-sectional and abottom view of the precursor of FIG. 3 comprising a sacrificial fiberstitched in accordance with the stitching method illustrated in FIG. 8;

FIG. 10 is a flowchart illustrating a method for manufacturing theperforated composite facing sheet of the noise attenuating device ofFIG. 1;

FIG. 11 is a schematic cross-sectional representation of an exemplaryperforated composite facing sheet of the noise attenuating device ofFIG. 1 manufactured in accordance with the method of FIG. 10; and

FIG. 12 is a flow diagram illustrating an exemplary embodiment of themethod of FIG. 10.

DETAILED DESCRIPTION

Aspects of various embodiments are described through reference to thedrawings.

The present disclosure relates to manufacturing of perforated compositeparts. Such composite parts may, for example, be part of noiseattenuating devices sometimes referred to as “acoustic liners” or“acoustic panels” for aircraft and other applications. In variousaspects, the present disclosure relates to manufacturing parts such asperforated facing sheets of noise attenuating devices that comprisecomposite materials including carbon fiber, glass fiber and/or naturalfiber reinforced structures. Noise attenuating devices such as thosereferenced herein may be suitable for use in aircraft engines, passengercabins of aircraft, trains, trucks or other vehicles, structuralframework/bodies of aircraft and other vehicles, and in industrial/civilor other applications requiring noise attenuation.

In some embodiments, the manufacturing of perforated composite partssuch as facing sheets for noise attenuating devices may comprise the useof sacrificial fiber(s) inserted in composite precursors andsubsequently removed to form one or more holes in the composite parts.The removal of the sacrificial fibers may, for example, comprisemechanically withdrawing the sacrificial fibers or causing thesacrificial fibers to disintegrate. The use of sacrificial fibers forforming holes in perforated facing sheets may have advantages overconventional hole forming methods (e.g., mechanical drilling, laserdrilling, grit blasting of a masked laminate). For example, in someembodiments, the use of sacrificial fibers may result in comparativelystronger composite parts because the holes do not cut through (i.e.,intersect, damage) the structural fibers of the parts, which couldotherwise occur using other conventional drilling methods. Also, theavoidance of damage to the structural fibers may also reduce the risk ofexposing cut sections of the structural fibers to moisture and therebyreduce the risk of fluid ingress and delamination. Further, in contrastwith some laser drilling methods, the use of sacrificial fibers asdescribed herein may not cause significant heat affected zones and localdelamination around the holes produced in the parts. These and otheradvantages will be apparent from the following description.

FIG. 1 is a partial axonometric view including a cutaway portion of anexemplary noise attenuating device 10 according to the presentdisclosure. Noise attenuating device 10 may comprise one or moreperforated facing sheets 12 (referred hereinafter as “facing sheet 12”),one or more honeycomb or other cellular cores 14 (referred hereinafteras “cellular core 14”) and one or more sound reflecting backing plates16 (referred hereinafter as “backing plate 16”). Cellular core 14 may bebonded between facing sheet 12 and backing plate 16. Cellular core 14may partition the space between facing sheet 12 and backing plate 16into a plurality of parallel cells 14A. Facing sheet 12 may comprise oneor more holes 18 extending therethrough. The number, size, shape andspacing of holes 18 may be selected according to known or other methodsto establish desired acoustic performance. In some embodiments, theholes 18 may be specified so that between about 5% to about 12% of thesurface area of facing sheet 12 is perforated. In some embodiments, theholes 18 may be selected so that between about 4% to about 10% of thesurface area of facing sheet 12 is perforated. In some embodiments, theholes 18 may be selected so that between about 5% to about 20% of thesurface area of facing sheet 12 is perforated. In some embodiments,backing plate 16 may also be perforated to allow the passage of heatedair for anti-icing purposes.

During use, facing sheet 12 may be facing a source of noise andattenuation of the sound waves that impinge facing sheet 12 may occuraccording to a number of mechanism such as: energy loss due to frictionwhen the sound waves penetrate facing sheet 12 through holes 18;pressure loss when the sound waves expand into cells 14A; and reactivecancellation of a sound wave entering and travelling in cell 14A by aprevious sound wave that has been reflected and is returning frombacking plate 16. In some embodiments, the depth of cells 14A (i.e.,thickness of core 14) may be selected (i.e., tuned) to attenuate adesired frequency or range of frequencies. Since a plurality of holes 18may be in communication with each of cells 14A, cells 14A may functionas a Helmholtz resonant cavity.

Noise attenuating devices having the construction shown in FIG. 1 may besuitable for use in aircraft engines. For example, noise attenuatingdevice 10 may be suitable for installation in a nacelle or other part ofan aircraft engine. For example, noise attenuating device 10 may bedisposed in selected positions within flow ducts of an aircraft engine.Such flow duct(s) may comprise the inlet duct, fan duct and/or thenozzle assembly of a nacelle. For example, noise attenuating device 10may be used as a lip acoustic liner/panel or an inlet acousticliner/panel. Noise attenuating device 10 may be part of a single-pieceor multi-piece acoustic liner/panel having a generally linear or curvedconfiguration. For example noise attenuating device 10 may be part of asingle-piece or a multi-piece annular-shaped acoustic liner/panel forinstallation into a nacelle of an aircraft engine and comprising a noiseattenuation region that extends substantially 360 degrees about acentral axis.

Noise attenuating device 10 shown in FIG. 1 may comprise a single degreeof freedom (hereinafter “SDOF”) acoustic liner/panel but aspects of thepresent application are equally applicable to double degree of freedom(hereinafter “2DOF”) acoustic liners/panels not specifically shownherein. For example in a 2DOF acoustic liner/panel, perforated facingsheet 12 may be backed by two layers of cellular separator 14 that areseparated from each other via a perforated septum sheet (not shown).

The acoustic performance of noise attenuating device 10 may be highlydependent on its construction including the specification of holes 18and also on the depth of cells 14A in cellular separator 14. Generally,noise attenuating devices of the types referenced herein can be designedto be most effective to reduce the effective perceived noise level andaccordingly the thickness of the cellular separator 14 (i.e., the spacebetween facing sheet 12 and backing plate 16) may be about 1-2 inches(25-50 mm).

FIG. 2A is a partial cross-sectional view of noise attenuating device 10taken along line 2-2 of FIG. 1 showing exemplary holes 18 extendingthrough facing sheet 12 of device 10 at an angle to normal axis “A” offacing sheet 12. An axis of one of the holes 18 is illustrated andlabelled as “H”.

FIG. 2B is a partial cross-sectional view of noise attenuating device 10taken along line 2-2 of FIG. 1 showing exemplary holes 18 extendingthrough facing sheet 12 of device 10 and having an axis “H”substantially parallel to normal axis “A” of facing sheet 12.

FIG. 3 is a schematic cross-sectional representation of an exemplaryprecursor 19 used in the manufacturing of perforated facing sheet 12 ofnoise attenuating device 10. Precursor 19 may comprise a preformincluding structural fibers 24 infused with matrix material 26 that hasbeen partially or fully cured. Even though the present disclosure ismainly directed to the manufacturing of perforated facing sheet 12, itis understood that precursor 19 and the methods disclosed herein may beused to manufacture other perforated composite parts having afiber-reinforced structure. Accordingly, references made herein tofacing sheet 12 are intended to be non-limiting. Precursor 19 may have asheet configuration and normal axis “A” as illustrated. Precursor 19 maycomprise two removable outer plies 20, a layup 22 of structural fibers24 embedded in a partially or fully cured matrix material 26 andinterposed between removable plies 20. Precursor 19 may also compriseone or more sacrificial fibers 28 (referred hereinafter as “sacrificialfiber 28”) extending through removable plies 20, matrix material 26 andbetween structural fibers 24. In some embodiments, a relatively thinrelease film may be applied between one or both removable plies 20 andlayup 22 (e.g., between faces 22A, 22B and their respective removableplies 20). The use of such release film may be beneficial in cases wherea smoother surface is desired at faces 22A and/or 22B.

The term “precursor” as used herein is intended to encompass a componentor an assembly of components that is used in the manufacturing of afinal composite part such as facing sheet 12 but that is at a (e.g.,pre-final) stage in the manufacturing process that precedes the finalcomposite part. For example, precursor 19 may comprise a preform orlaminate of the final composite part. For example, precursor 19 maycomprise dry layers of structural fibers 24 (e.g., woven or non-crimpfabrics), dry layers of structural fibers 24 with sacrificial fiber 28inserted therebetween, layup 22 of structural fibers 24 and sacrificialfiber 28 infused with matrix material 26 that has been partially orfully cured, layup 22 of structural fibers 24 and sacrificial fiber 28embedded in cured matrix material 26 prior to removal of sacrificialfiber 28. In some embodiments, precursor 19 shown in FIG. 3 may be in acured laminate form.

Layup 22 may comprise first face 22A and opposite second face 22Bbetween which structural fibers 24 embedded in a cured matrix material26 may be interposed. First face 22A may represent a top face of facingsheet 12 facing a source of noise and second face 22B may represent anopposite bottom face of facing sheet 12 facing backing plate 16.Sacrificial fiber 28 may extend across the thickness of layup 22 andthrough first face 22A and second face 22B.

Removable outer plies 20 may comprise a suitable release medium that istypically used during the manufacture of fiber-reinforced compositematerials. Accordingly, removable outer plies 20 may be removablyattached to layup 22. For example, removable outer plies 20 may beconfigured to not chemically bond to matrix material 26 so that it maybe easily removed by peeling after curing of matrix material 26. Forexample, outer plies 20 may each comprise a cohesively formed plasticmesh comprising openings therethrough and that does not readily adhereto other polymers. Such openings may permit matrix material 26 topermeate therethrough during infusion of matrix material 24 (e.g.,resin) into layup 22 of structural fibers 24. In some embodiments,removable outer plies 20 may each comprise a polytetrafluoroethylene(PTFE) coated fiberglass fabric of the type sold under the trade nameRELEASE EASE. In some embodiments outer plies 20 may comprise a wovenmedium where the weave is porous and offers acceptable tear resistancethat permits removal of outer plies 20 by peeling and also allows forshearing of sacrificial fiber 28. Arrows “P” illustrate the peeling ofremovable outer plies 20 from precursor 19.

In some embodiments, one of removable outer plies 20 may be of the typeknown as “wet” peel ply which can facilitate tacking onto a tool (e.g.,mandrel, mold) that is used for preforming. In such cases the insertionof sacrificial fiber 28 into precursor 19 could be conducted afterpreforming.

Precursor 19 may be produced using known or other manufacturing methodssuitable for producing fiber-reinforced structures. For example,precursor 19 may comprise pre-impregnated structural fibers 24 that aresubsequently heated to cause bonding and curing of precursor 19.Alternatively or in addition, precursor 19 may comprise dry structuralfibers 24 that are subsequently infused with matrix material 26 using aknown or other resin infusion process(es) such as, for example, resintransfer infusion (RTI), resin transfer molding (RTM), vacuum-assistedresin transfer molding (VARTM), vacuum-assisted resin infusion (VARI),autoclave assisted resin infusion (AARI), single line injection (SLI),resin film infusion (RFI) and Seemann composites resin infusion moldingprocess (SCRIMP). Such resin infusion process(es) may be conducted in orout of an autoclave. In some situations, it may be preferable to insertsacrificial fiber 28 through a precursor 19 that has dry structuralfibers 24 as opposed to pre-impregnated structural fibers 24 becausepre-impregnated structural fibers 24 may cause some of the matrixmaterial 26 to build up on needles that are used during stitching.

Matrix material 26 may be of any known or other type suitable forproducing fiber-reinforced structures. For example, matrix material 26may have a curing/gel temperature (e.g., <150° C.) i.e., between B stageand C stage, that is lower than the melting temperature of sacrificialfiber 28. In various embodiments, matrix material 26 may comprisepolyester, vinyl-ester, epoxy, benzoxanine and/or bismaleimide. Somematrix materials 26 having a good fire, smoke and toxicity (FST)properties may be suitable for “in cabin” transportation applications.For example, depending on the specific application and requirements,matrix material 26 may comprise one of the following products: productname T-PRIME 160 sold under the trade name GURIT; product name 337 soldunder the trade name EPO-TEK; product name TOOLFUSION 3 sold under thetrade name TYGAVAC; product name RENLAM LY120 sold under the trade nameHUNTSMAN; product names ARALDITE LY1564, ARALDITE FST 40002, ARALDITEFST 40003 and ARADUR 2594 sold under the trade name HUNTSMAN; productnames CYCOM 890 and CYCOM 5250-4 sold under the trade name CYTEK;product names RTM 6 and RTM 651 sold under the trade name HEXCEL;product name EPON 862 sold under the trade name MOMENTIVE; product namesLOCTITE BZ 9120 and LOCTITE BZ 9121 sold under the trade name HENKEL;and, product name BMI-1 sold under the trade name RAPTOR RESINS.

In some embodiments, sacrificial fiber 28 may be configured to evaporateat a temperature that is not otherwise detrimental to precursor 19. Forexample, sacrificial fiber 28 may comprise a thermoplastic aliphaticpolyester. For example, sacrificial fiber 28 may comprise polylacticacid or polylactide (PLA) (e.g., 0.5 mm diameter and a meltingtemperature of about 160° C.) having the molecular formula (C₃H₄O₂)_(n)and being a biodegradable thermoplastic aliphatic polyester derived fromrenewable resources, such as corn starch, tapioca roots, chips orstarch, or sugarcane. For example, sacrificial fiber 28 may comprise oneof: polyacrylamides, polyacrylates, acrylamide-dimethylaminoethylacrylate copolymers, polyamines, polyethyleneimines, polyamidoamines andpolyethylene oxide. In some embodiments, matrix material 26 may becured/gelled to a level between the B stage and the C stage prior toremoval of sacrificial fiber 28 so that the removal of sacrificial fiber28 by evaporation may subsequently cause full curing of matrix material26.

Alternatively, sacrificial fiber 28 may be configured to be dissolvedusing a solvent that is not otherwise detrimental to precursor 19. Forexample, sacrificial fiber 28 may be water-soluble. In some embodiments,sacrificial fiber may comprise one of: water soluble polyethylene oxide,hydrolysed cellulose acetate and polyvinyl alcohol.

FIG. 4 illustrates exemplary cross-sectional shapes for sacrificialfiber 28 inserted into precursor 19. Sacrificial fiber 28 may comprise amonofilament produced by extrusion. Sacrificial fiber 28 may have agenerally circular or a non-circular cross-sectional profile. Themaximum cross-sectional dimension (e.g., diameter) and shape ofsacrificial fiber 28 may be generally equivalent to the size and shapeof holes 18 to be formed in facing sheet 12 to achieve the desiredacoustic performance. For example, in various applications, sacrificialfiber 28 may have a maximum cross-sectional dimension between about 0.08mm to about 2 mm. In some embodiments, sacrificial fiber 28 may be partof a sacrificial yarn comprising a plurality of sacrificial fibers 28.Sacrificial fiber 28 may be in the form of a continuous monofilament ormay be part of an assembly of continuous filaments in the form of a towor twisted together. In some embodiments, sacrificial fiber 28 may behollow.

FIG. 5 is an exploded view of an exemplary layup 22 of structural fibers24 and removable outer plies 20 of the precursor 19 of FIG. 3. Layup 22of structural fibers 24 may comprise a plurality of fabric plies24A-24D. In some embodiments, one or more of fabric plies 24A-24D maycomprise non-crimp fabric. Layup 22 may comprise additional or fewerfabric plies 24A-24D than those shown herein depending on the specificapplication and requirements. For example, plies 24A-24C of layup 22 maycomprise 5 harness carbon weave plies having an architecture of 0/90,+/−0.45 and 0/90 respectively. Ply 24D may comprise one of: a 120 stylefiberglass fabric; an uncured resin resurfacer; a fiberglass veil orfleece; a thermoplastic veil or fleece; a thermoplastic film that issubstantially stable up to 200° C.; a thin (e.g., 0.002″ or 0.05 mm)polyethersulfone (PES) film; a thin (e.g., 0.002″ or 0.05 mm)polyethersulfone (PES) film; a thin (e.g., 0.002″ or 0.05 mm) polyamides(PA) film; and, a thin (e.g., 0.002″ or 0.05 mm) (PTFE) film. Ply 24Dmay be Corona (i.e., plasma) treated and may be clear or pigmented. Suchtreatment may provide additional UV and abrasion resistance and may insome applications eliminate the need for painting. Depending on theapplication ply 24D may not be required. In some applications, anadditional ply of the same or similar construction to that of ply 24Dmay be disposed between ply 24A and removable outer ply 20.

The fabric in one or more of plies 24A-24D may be bindered with anun-catalyzed epoxy powder or other powder compatible with matrixmaterial 26 which may be activated at a preforming temperature (e.g.,between 90° C. and 130° C.) which may be lower than the curingtemperature. After preforming, layup 22 may be sufficiently solid andfacilitate the introduction of sacrificial fiber 28 in precursor 19 bystitching as described below. Alternatively, sacrificial fiber 28 may beinserted into precursor 19 without requiring heating precursor 19 toactivate the binder. In some embodiments, sacrificial fiber 28 may notcomprise a weft nor a warp thread. Layup 22 and removable outer plies 20may be assembled using a non-crimp fabric (NCF) machine sold under thetrade names LIBA or KARL MAYER and stitched together using a warp knit,tufting or other stitch style/pattern using sacrificial fiber 28. Thestitch style and density may be selected based on the handling abilityof layup 22, the amount of perforation desired in facing sheet 12 andalso the acoustic performance desired from facing sheet 12. Depending onthe machine used, the stitch pattern (e.g., chain, tricot, modifiedtricot, blind stitching, tufting, warp-knitting, etc.), the frequency(e.g., courses per inch in the roll direction or 0° axis), and gauge(rows of stitching across the roll width) may be selected. In someembodiments, sacrificial fiber 28 may be inserted (e.g., stitched) indry fabric plies 24A-24D.

FIG. 6 shows the application of a non-limiting exemplary stitch ofsacrificial fiber 28 using stitching needles through both removableouter plies 20 and also through structural fibers 24 of precursor 19.The application of sacrificial fiber 28 by stitching may result insacrificial fiber 28 being inserted between structural fibers 24 withoutdamaging structural fibers 24. For example, the needles may deflectstructural fibers 24 or yarns without breaking or otherwise damagingthem in order to insert sacrificial fiber 28 therebetween. In thisparticular embodiment, both stitching needles may be manipulated fromthe same side of precursor 19. Using the stitching method shown in FIG.6, the angle of sacrificial fiber 28 from normal axis A (shown in FIG.2) may be varied between 0 degrees (e.g., parallel) from axis “A” toabout 45 degrees from axis “A”, The stitching method illustrated in FIG.6 may also be referred to as “one side stitching”.

FIG. 7 is an axonometric view of an exemplary stitch of sacrificialfiber 28 obtained with the stitching method illustrated in FIG. 6.

FIG. 8 illustrates the application of another exemplary stitch ofsacrificial fiber 28 through removable outer plies 20 and also throughstructural fibers 24 of precursor 19. The application of sacrificialfiber 28 is illustrated in three steps labeled as 1, 2 and 3. Thestitching process illustrated in FIG. 8 may also be referred to as“tufting”. A support foam backing 30 may be used for supportingprecursor 19 during stitching and may permit the needle(s) to penetratethrough the thickness of precursor 19 without damaging to the needles.Instead of support foam backing 30, a more rigid support structurehaving a slot to permit the passage of the needle(s) could be used.

FIGS. 9A, 9B and 90 respectively show a top, a cross-sectional and abottom view of precursor 19 comprising sacrificial fiber 28 that hasbeen stitched in accordance with the stitching method illustrated inFIG. 8.

FIG. 10 is a flowchart illustrating an exemplary method 100 formanufacturing a perforated composite part such as composite facing sheet12 of noise attenuating device 10. Method 100 may comprise producingand/or using precursor 19 as shown in FIG. 3. For example, in someembodiments, method 100 may comprise: producing precursor 19 comprisingstructural fibers 24 embedded in a cured matrix material 26 andinterposed between two removable plies 20 where precursor 19 alsocomprises one or more sacrificial fibers 28 extending through removableplies 20, matrix material 26 and between structural fibers 24 (see block102); removing at least one of the removable plies 20 from precursor 19(see block 104); and removing sacrificial fiber(s) 28 from precursor 19after removing the at least one of removable plies 20 to form one ormore through holes 18 in precursor 19.

In some embodiments of method 100, it may be desirable to conductnon-destructing inspection (NDI) on precursor 19 before removingsacrificial fiber 28. For example, it may be desirable to conduct one ormore NDI-related scans (e.g., ultrasound, radiography) on precursor 19while there are no holes 18 in precursor 19 so that data obtained fromsuch scan(s) may be easier to interpret.

Removing of sacrificial fiber 28 may comprise mechanically withdrawingsacrificial fiber 28 from precursor 19, melting sacrificial fiber 28 andevacuating sacrificial fiber 28, or, causing sacrificial fiber 28 todisintegrate (e.g., evaporation, dissolution).

As explained above, producing precursor 19 may comprise forming layup 22comprising structural fibers 24 and infusing matrix material 26 (e.g.,resin) between the structural fibers 24. Producing precursor 19 may alsocomprise inserting sacrificial fiber 28 into precursor 19 prior toinfusing matrix material 26 between structural fibers 24.

Alternatively, instead of using a resin infusion process, structuralfibers 24 that are used for producing precursor 19 may bepre-impregnated with matrix material 26 and heated to cause bonding andcuring of precursor 19. In such case, sacrificial fiber 28 may beinserted between structural fibers 24 of precursor 19 prior to curingmatrix material 26. Insertion of sacrificial fiber 28 between structuralfibers 24 and through removable outer plies 20 may comprise known orother stitching techniques. For example, the insertion of sacrificialfiber 28 may comprise tufting and/or warp knitting. In some embodiments,the insertion of sacrificial fiber 28 into precursor 19 may be conductedin accordance with the teachings of U.S. Pat. No. 5,490,602, the entirecontents of which being incorporated herein by reference.

Removable outer plies 20 may each comprise a release ply such as, forexample, a polytetrafluoroethylene-coated fiberglass fabric/mesh or dryweaves of polyamide (nylon) or that are polyester treated so as tofacilitate subsequent removal by peeling. In various embodiments, outerplies 20 may comprise light to heavy weight woven fabrics made of nylonor polyester. In some embodiments, outer ply(ies) 20 may comprise anylon woven release fabric such as product number 60B or 60BR sold underthe trade name TYGAVAC.

The removal of outer plies 20 may comprise peeling outer plies 20 awayfrom structural fibers 24 and matrix material 26 as illustrated in FIG.3 (see arrows P). Since sacrificial fiber 28 may extend through thethickness of precursor 19 (e.g., through and between first surface 22Aand second surface 22B) and through outer plies 20, the removal of outerplies 20 may cause severing of sacrificial fiber 28 so as to expose theends of sacrificial fiber 28 (i.e., on each side across the thickness ofprecursor 19) and facilitate disintegration of sacrificial fiber 28. Forexample, since sacrificial fiber 28 may be stitched through removableouter plies 20, the removal of plies 20 may cause portions ofsacrificial fiber 28 extending outside of layup 22 to be broken off fromportions of sacrificial fiber 28 extending inside (i.e., through) layup22. In some cases, sacrificial fiber 28 may be severed near or at firstsurface 22A and/or second surface 22B. Accordingly, removable outerplies 20 may also be referenced as fiber-severing members. The removalof outer plies 20 may also cause the removal of kinked, looped orknotted portions of sacrificial fiber 28 that may have been producedfrom the stitching process. Exposing the opposite ends of sacrificialfiber 28 by severing may facilitate the removal of sacrificial fiber 28by evaporation or dissolution from both ends of sacrificial fiber 28extending through layup 22.

Depending on the materials involved, the peeling of outer ply(ies) 20may alternatively cause the complete removal of sacrificial fiber 28from precursor 19 by causing sacrificial fiber 28 to be pulled out fromprecursor 19 and thereby eliminate the need for subsequentdisintegration or evaporation of sacrificial fiber 28. In someembodiments, the use of a sacrificial fiber 28 of smaller diameter mayfacilitate the peeling of outer ply(ies) 20.

Instead of or in addition to removable outer plies 20, one or more othertypes of severing members may also be suitable for the purpose ofsevering sacrificial fiber 28 prior to the removal of sacrificial fiber28 by evaporation, dissolution or other method. For example, a suitablesevering member may comprise a severing fiber, yarn or cord engaged withsacrificial fiber 28 so that the removal of the severing fiber/yarn/cordmay cause severing of sacrificial fiber 28. For example, such severingfiber/yarn/cord could be integrated with precursor 19 during thestitching of sacrificial fiber 28 or at some other time. In someembodiments, such severing member(s) could include some other material(e.g., in the form of a strip) that may be removably attached toprecursor 19 for the purpose of causing severing of sacrificial fiber 28when removed.

In any case, such severing member(s) may be removed manually or with theassistance of a suitable tool.

In some embodiments, it may be sufficient to only remove one of the tworemovable outer plies 20 prior to removing sacrificial fiber 28 fromlayup 22 by evaporation or dissolution. For example, evaporation ordissolution of sacrificial fiber 28 from a single end (i.e., from asingle side of precursor 19) may be acceptable in some circumstances.

Disintegration of structural fiber 28 may cause the formation of one ormore through holes 18 extending across the thickness of facing sheet 12.The thickness of facing sheet 12 as referenced herein may be consideredalong normal axis A of facing sheet 12 and/or precursor 19. However, asexplained above, holes 18 may be oriented either substantially parallelto or at an angle from normal axis A. Holes 18 may follow the pathformerly followed by sacrificial fiber 28 through precursor 19. In someembodiments, holes 18 may follow a substantially entirely linear path.Alternatively, in some embodiments, holes 18 could follow a curved path.In any case, holes 18 formed by the disintegration of sacrificial fiber28 may be substantially high-fidelity replicas of the diameter andtrajectory of sacrificial fiber 28.

In some embodiments, the disintegration of sacrificial fiber 28 may beconducted according to methods described in U.S. Pat. No. 5,490,602and/or U.S. Patent Application Publication No. 2013/0065042 A1, theentire contents of both of which being incorporated herein by reference.Depending on the material of sacrificial fiber 28, disintegration ofsacrificial fiber 28 may be conducted by evaporation or by dissolution.Evaporation of sacrificial fiber 28 may comprise heating precursor 19 toa temperature and duration that are sufficient to cause evaporation ofsacrificial fiber 28 but that are not otherwise detrimental tostructural fibers 24 or to matrix material 26. The evaporation processmay comprise maintaining a sufficiently high temperature for a period oftime sufficient to achieve satisfactory removal of sacrificial fiber 28.In order to accelerate the evaporation process, fluids (e.g., air)surrounding precursor 19 may be circulated to provide ventilation.Alternatively or in addition, precursor 19 may be enclosed in a vacuumbag during such evaporation and the bag may be continuously orintermittently evacuated during the evaporation.

Dissolution of sacrificial fiber 28 may comprise exposing precursor 19to a solvent that causes dissolution of sacrificial fiber 28 but that isnot otherwise detrimental to the structural fibers 24 or to matrixmaterial 26. In some embodiments, sacrificial fiber 28 may bewater-soluble. In some cases, a small amount of residue from sacrificialfiber 28 may remain inside of holes 18 and such residue may be removedusing a flow of pressurized air or water for example.

In some embodiments, sacrificial fiber 28 may be coated with an agentthat hinders a chemical reaction between sacrificial fiber 28 and matrixmaterial 26. Such agent may comprise a suitable release agent or aninert elastomeric urethane, silicone or acrylic dip, liquid glass or aconformal barrier such as that sold under the trade name PARYLENE. Theuse of such agent may facilitate the removal of sacrificial fiber 28 byevaporation or dissolution. In some cases, the use of such agent maycause sacrificial fiber 28 to be entirely or partially pulled out fromprecursor 19 when removable outer plies 20 are peeled. In cases wheresacrificial fiber 28 is not entirely removed from precursor 19 whenpeeling removable outer plies 20, it may be desirable to remove theremainder of sacrificial fiber 28 by evaporation or dissolution asdescribed above.

FIG. 11 is a partial schematic cross-sectional representation of anexemplary perforated composite facing sheet 12 of the noise attenuatingdevice 10 of FIG. 1 manufactured in accordance with the method 100 ofFIG. 10 using precursor 19. FIG. 11 shows composite facing sheet 12after matrix material 26 has been cured, removable plies 20 have beenremoved and sacrificial fiber 28 has been removed in order to formthrough holes 18. As explained below, holes 18 may extend through thethickness (i.e., across axis A) of facing sheet 12. Holes 18 may followa substantially linear (straight) trajectory. Alternatively, holes 18may follow a curved trajectory. Holes 18 may extend substantiallyparallel to axis A so as to follow the shortest path across thethickness of facing sheet 12. Alternatively, holes 18 may be oriented atan incline relative to axis A.

FIG. 12 is a flow diagram illustrating an exemplary embodiment of themethod 100 of FIG. 10. The top of FIG. 12 illustrates an embodiment ofblock 102 of method 100 where precursor 19 is produced. For example, thefirst (i.e., top) step in FIG. 12 shows flat plies of structural fibers24 (i.e., see 24A-24D shown in FIG. 5) and removable outer plies 20being overlaid. The insertion of sacrificial fiber 28 into precursor 19by stitching may be conducted either before preforming (e.g., see 102A)or after preforming (e.g., see 102B). Reference numeral 102A illustratesthat sacrificial fiber 28 may be inserted through the flat plies bystitching and precursor 19 may be subsequently preformed into a shapeapproximating the final shape of facing sheet 12. For example, precursor19 may be preformed into a single-piece annular configuration aftersacrificial fiber 28 has been stitched through the plies. Alternatively,reference numeral 102B shows that precursor 19 may be preformed into thesingle-piece annular configuration and sacrificial fiber 28 may besubsequently added to precursor 19 by stitching along a curved surface.

In some embodiments, depending on the type of material used assacrificial fiber 28, it may be desirable to conduct the stitching at atemperature that temporarily softens the material of sacrificial fiber28. The elevation of temperature during stitching may be particularlyuseful when a polymeric monofilament of relatively large diameter andstiffness is used as sacrificial fiber 28.

Reference numeral 104 illustrates the removal of one of removable outerplies 20 by peeling. As explained above, the removal of outer plies 20(or other suitable fiber severing member) may cause severing ofsacrificial fiber 28 as illustrated in FIG. 3 to expose one or more endsof sacrificial fiber 28.

In some embodiments, depending on the type of material used assacrificial fiber 28, it may be possible to facilitate the peeling ofouter plies 20 by first weakening sacrificial fiber 28 using a householdclothes iron or any other suitable means of applying heat and/orpressure to sacrificial fiber 28. For example, a heated clothes iron maybe pressed against the inner and/or outer sides of precursor 19 afterthe stitching of sacrificial fiber 28 through precursor 19. In the caseof sacrificial fiber 28 being made of a polymer (or some other materialthat may be weakened by heat and/or pressure), the application of heatmay weaken the molecular structure of the polymer. The application ofpressure may also cause flattening of the portions of sacrificial fiber28 extending across the inner and/or outer surfaces of precursor 19thereby further weakening sacrificial fiber 28 and thereby facilitatingshearing of sacrificial fiber 28 when outer ply(ies) 20 is/aresubsequently peeled. Accordingly, the temperature of the clothes ironshould be lower than the melting point of sacrificial fiber 28 but highenough to weaken the molecular structure of the material of sacrificialfiber 28. The ironing of sacrificial fiber 28 may be conducted afterstitching but before preforming of precursor 19. Accordingly, theflattening of the portions of sacrificial fiber 28 extending across theinner and/or outer surfaces of precursor 19 may increase the area ofsacrificial fiber 28 facing precursor 19 and thereby reduce thepenetration of sacrificial fiber 28 into the inner/outer surfaces ofprecursor 19 during preforming. Accordingly, the flattening and/orweakening of sacrificial fiber 28 may reduce the indentation ofprecursor 19 caused by sacrificial fiber 28 during preforming.

After the removal of one or more of removable outer plies 20,sacrificial fiber 28 may be removed by evaporation (e.g., see 106A) ordissolution (e.g., see 106B). Reference numeral 106A shows thatprecursor 19 may then be heated in a ventilated heating chamber at atemperature and for a duration sufficient to achieve a desired amount ofremoval of sacrificial fiber 28 from precursor 19 by evaporation asexplained above. Alternatively, reference numeral 106B shows thatprecursor 19 may be exposed to a solvent (e.g., water) for a durationsuitable to achieve a desired amount of removal of sacrificial fiber 28from precursor 19 by dissolution as explained above. In someembodiments, it may be desirable to heat and agitate the solvent toaccelerate the dissolution of sacrificial fiber 28. In some embodimentsusing water as a solvent, it may be desirable to have the water heatedto a temperature of around 95° C. during dissolution. In someembodiments, the water may be heated to a temperature between 90° C. and95° C. In some embodiments, using water that is slightly alkaline oracidic may accelerate the dissolution of sacrificial fiber 28.

After sacrificial fiber 28 has been substantially removed from precursor19, facing sheet 12 in the form shown in FIG. 11 may be obtained.Alternatively, precursor 19 may require subsequent processing in orderto obtain a final and functional composite part. For example, referencenumeral 108 illustrates a further step of drying precursor 19 aftersacrificial fiber 28 has been substantially removed from precursor 19.Further processing of precursor 19 after the removable of sacrificialfiber 28 may not be necessary but in some cases drying of precursor 19may be desired to remove the solvent from precursor 19 after dissolutionof sacrificial fiber 28.

The above description is meant to be exemplary only, and one skilled inthe relevant arts will recognize that changes may be made to theembodiments described without departing from the scope of the inventiondisclosed. For example, the blocks and/or operations in the flowchartsand drawings described herein are for purposes of example only. Theremay be many variations to these blocks and/or operations withoutdeparting from the teachings of the present disclosure. For instance,the blocks may be performed in a differing order, or blocks may beadded, deleted, or modified. The present disclosure may be embodied inother specific forms without departing from the subject matter of theclaims. Also, while the devices, facing sheets, precursors and methodsdisclosed herein and shown herein may comprise a specific number ofelements/steps, the devices, facing sheets, precursors and methods couldbe modified to include additional or fewer of such elements/steps. Thepresent disclosure is also intended to cover and embrace all suitablechanges in technology. Modifications which fall within the scope of thepresent invention will be apparent to those skilled in the art, in lightof a review of this disclosure, and such modifications are intended tofall within the appended claims. Also, the scope of the claims shouldnot be limited by the preferred embodiments set forth in the examples,but should be given the broadest interpretation consistent with thedescription as a whole.

What is claimed is:
 1. A precursor for manufacturing a perforatedcomposite part, the precursor comprising: a layup having a first faceand an opposite second face, the layup comprising structural fibersembedded in a cured matrix material and interposed between the firstface and the second face; and a sacrificial fiber extending through thelayup and through the first face and the second face of the layup, thesacrificial fiber being removable from the layup in order to form athrough hole in the layup at a location of the sacrificial fiber; and afiber severing member removably attached to the layup and configured tosever the sacrificial fiber upon removal of the fiber severing memberfrom the layup, wherein the fiber severing member comprises a firstremovable outer ply disposed against the first face of the layup.
 2. Theprecursor as defined in claim 1, comprising a second removable outer plydisposed against the second face of the layup.
 3. A precursor formanufacturing a perforated composite part, the precursor comprising: alayup having a first face and an opposite second face, the layupcomprising structural fibers embedded in a cured matrix material andinterposed between the first face and the second face; and a sacrificialfiber extending through the layup and through the first face and thesecond face of the layup, the sacrificial fiber being removable from thelayup in order to form a through hole in the layup at a location of thesacrificial fiber; and a fiber severing member removably attached to thelayup and configured to sever the sacrificial fiber upon removal of thefiber severing member from the layup, wherein the fiber severing memberis configured to not chemically bond with the matrix material.
 4. Aprecursor for manufacturing a perforated composite part, the precursorcomprising: a layup having a first face and an opposite second face, thelayup comprising structural fibers embedded in a cured matrix materialand interposed between the first face and the second face; and asacrificial fiber extending through the layup and through the first faceand the second face of the layup, the sacrificial fiber being removablefrom the layup in order to form a through hole in the layup at alocation of the sacrificial fiber; and a fiber severing member removablyattached to the layup and configured to sever the sacrificial fiber uponremoval of the fiber severing member from the layup, wherein the fibersevering member comprises a polytetrafluoroethylene-coated fiberglassfabric.